Valence electron spectroscopy using soft X-ray emission spectroscopy electron microscopes

Compact soft-X-ray emission spectroscopy (SXES) instrument, which was first applied to transmission electron microscope, was recently applied to scanning electron microscope and electron-probe microanalyzer, which improved the practical applicability of SXES as a tool for investigating chemical bonding state of elements in bulk materials. Intensity profiles of Al-L, B-K and Si-L emission spectra, which directly reflect the partial density of state of valence band (VB), were explained. Those energy positions are affected by core-level shift (chemical shift, CS) and a change of density of state (DOS) of VB, for example a bandgap formation. Those VB DOS measurements, combined with electron-beam scanning technique, can conduct a chemical bond mapping of a bulk material. It was presented that L-emission spectra of 3d transition-metal elements give DOS+CS information in Lα,β emission, dielectric information in Lℓ,η, and the number of 3d electrons in the integrated intensity ratio of Lα,β/(Lα,β+ Lℓ,η). Since the electron-beam excited SXES experiment for bulk specimens can control the self-absorption effect, L-absorption profile of 3d-TM elements is obtainable from L-emission measurements by changing the accelerating voltage. Furthermore, CB information can be obtained from SXES spectra of semiconductor materials; Si and diamond cases were presented, by using the self-absorption effect on the background intensity of bremsstrahlung (BS) caused by electron-beam irradiation of the specimen.